Due to the monthly nature of comics, and possibly also due to the fact that the schedule for new episodes is a thing in flux, the Young Justice tie-in comic is really taking its time in catching up with the show. In the latest issue, #7, we finally reach the point where Artemis joins the cast, as we see the events that led up to her secretly helping the team against Amazo.

...which leads to her finding Robin, Kid Flash, and Superboy up against Amazo.